Solvent cement welds thermoplastic sheets and piping by softening the surface of the material being bonded. Unlike gluing, which hardens to hold material together, the material softened by this substance trades molecules to form a solvent welded joint that has the strength of the parent material. Primers and proper preparation allow the solvent to form a bond without contamination from grease, inks and oils. beyond proper cleaning, the type of solvent cement must be compatible with the thermoplastic or the surface of the plastic will not melt correctly and the joint will not have a strong bond.
A list of compatible plastics will be listed on the solvent cement canister label. The three-letter designation listed on the canister label must match the three-letter designation printed on the surface of the thermoplastic to ensure a finished solvent welded joint has the strength to hold the amount of pressure required of the connection. Common three-letter plastic identifications are polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC) and acrylonitrile butadiene styrene (ABS). One thing all thermoplastic solvent cements have in common is the strong fumes emitted from the chemical during use.
The chemicals used to soften the surface of the three common thermoplastics have a strong odor that can become overpowering in the confined areas in which they are used. Proper ventilation will provide a constant flow of fresh air that keeps the solvent fumes from building in the area and reduce the chances of the user succumbing to asphyxiation. When a canister of solvent cement is opened and a strong odor cannot be smelled, the liquid cement inside the canister may have dried out or been frozen at one time.
Common signs that solvent cement has gone bad are a gel-like consistency, lumps floating inside the canister or a dauber that cannot be removed from the canister. Unlike paints or other solvent-based materials, solvent cements cannot be thinned to bring them back to their original consistency. Thinning this substance will cause the solvents used to soften the surface of plastics to break down and not allow a strong bond to form between the pieces of material. Cold is another factor that inhibits the cement’s ability to bond with plastic. The optimal temperature to apply solvent cement to a thermoplastic will be printed on the canister label, and the product should not be applied in temperatures sitting outside the optimal temperature range.